// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Diagnostics;
using System.Threading.Tasks;
using System.Xml.Schema;
using System.Xml.XPath;

namespace System.Xml
{
    // Represents a writer that provides fast non-cached forward-only way of generating XML streams containing XML documents
    // that conform to the W3C Extensible Markup Language (XML) 1.0 specification and the Namespaces in XML specification.
    public abstract partial class XmlWriter : IDisposable, IAsyncDisposable
    {
        // Write methods
        // Writes out the XML declaration with the version "1.0".

        public virtual Task WriteStartDocumentAsync()
        {
            throw new NotImplementedException();
        }

        //Writes out the XML declaration with the version "1.0" and the specified standalone attribute.

        public virtual Task WriteStartDocumentAsync(bool standalone)
        {
            throw new NotImplementedException();
        }

        //Closes any open elements or attributes and puts the writer back in the Start state.

        public virtual Task WriteEndDocumentAsync()
        {
            throw new NotImplementedException();
        }

        // Writes out the DOCTYPE declaration with the specified name and optional attributes.

        public virtual Task WriteDocTypeAsync(string name, string? pubid, string? sysid, string? subset)
        {
            throw new NotImplementedException();
        }

        // Writes out the specified start tag and associates it with the given namespace and prefix.

        public virtual Task WriteStartElementAsync(string? prefix, string localName, string? ns)
        {
            throw new NotImplementedException();
        }

        // Closes one element and pops the corresponding namespace scope.

        public virtual Task WriteEndElementAsync()
        {
            throw new NotImplementedException();
        }

        // Closes one element and pops the corresponding namespace scope. Writes out a full end element tag, e.g. </element>.

        public virtual Task WriteFullEndElementAsync()
        {
            throw new NotImplementedException();
        }

        // Writes out the attribute with the specified prefix, LocalName, NamespaceURI and value.
        public Task WriteAttributeStringAsync(string? prefix, string localName, string? ns, string? value)
        {
            Task task = WriteStartAttributeAsync(prefix, localName, ns);
            if (task.IsSuccess())
            {
                return WriteStringAsync(value).CallTaskFuncWhenFinishAsync(thisRef => thisRef.WriteEndAttributeAsync(), this);
            }

            return WriteAttributeStringAsyncHelper(task, value);
        }

        private async Task WriteAttributeStringAsyncHelper(Task task, string? value)
        {
            await task.ConfigureAwait(false);
            await WriteStringAsync(value).ConfigureAwait(false);
            await WriteEndAttributeAsync().ConfigureAwait(false);
        }

        // Writes the start of an attribute.

        protected internal virtual Task WriteStartAttributeAsync(string? prefix, string localName, string? ns)
        {
            throw new NotImplementedException();
        }

        // Closes the attribute opened by WriteStartAttribute call.

        protected internal virtual Task WriteEndAttributeAsync()
        {
            throw new NotImplementedException();
        }

        // Writes out a <![CDATA[...]]>; block containing the specified text.

        public virtual Task WriteCDataAsync(string? text)
        {
            throw new NotImplementedException();
        }

        // Writes out a comment <!--...-->; containing the specified text.

        public virtual Task WriteCommentAsync(string? text)
        {
            throw new NotImplementedException();
        }

        // Writes out a processing instruction with a space between the name and text as follows: <?name text?>

        public virtual Task WriteProcessingInstructionAsync(string name, string? text)
        {
            throw new NotImplementedException();
        }

        // Writes out an entity reference as follows: "&"+name+";".

        public virtual Task WriteEntityRefAsync(string name)
        {
            throw new NotImplementedException();
        }

        // Forces the generation of a character entity for the specified Unicode character value.

        public virtual Task WriteCharEntityAsync(char ch)
        {
            throw new NotImplementedException();
        }

        // Writes out the given whitespace.

        public virtual Task WriteWhitespaceAsync(string? ws)
        {
            throw new NotImplementedException();
        }

        // Writes out the specified text content.

        public virtual Task WriteStringAsync(string? text)
        {
            throw new NotImplementedException();
        }

        // Write out the given surrogate pair as an entity reference.

        public virtual Task WriteSurrogateCharEntityAsync(char lowChar, char highChar)
        {
            throw new NotImplementedException();
        }

        // Writes out the specified text content.

        public virtual Task WriteCharsAsync(char[] buffer, int index, int count)
        {
            throw new NotImplementedException();
        }

        // Writes raw markup from the given character buffer.

        public virtual Task WriteRawAsync(char[] buffer, int index, int count)
        {
            throw new NotImplementedException();
        }

        // Writes raw markup from the given string.

        public virtual Task WriteRawAsync(string data)
        {
            throw new NotImplementedException();
        }

        // Encodes the specified binary bytes as base64 and writes out the resulting text.

        public virtual Task WriteBase64Async(byte[] buffer, int index, int count)
        {
            throw new NotImplementedException();
        }

        // Encodes the specified binary bytes as bin hex and writes out the resulting text.
        public virtual Task WriteBinHexAsync(byte[] buffer, int index, int count)
        {
            return BinHexEncoder.EncodeAsync(buffer, index, count, this);
        }

        // Flushes data that is in the internal buffers into the underlying streams/TextReader and flushes the stream/TextReader.

        public virtual Task FlushAsync()
        {
            throw new NotImplementedException();
        }

        // Scalar Value Methods

        // Writes out the specified name, ensuring it is a valid NmToken according to the XML specification
        // (http://www.w3.org/TR/1998/REC-xml-19980210#NT-Name).
        public virtual Task WriteNmTokenAsync(string name)
        {
            ArgumentException.ThrowIfNullOrEmpty(name);
            return WriteStringAsync(XmlConvert.VerifyNMTOKEN(name, ExceptionType.ArgumentException));
        }

        // Writes out the specified name, ensuring it is a valid Name according to the XML specification
        // (http://www.w3.org/TR/1998/REC-xml-19980210#NT-Name).
        public virtual Task WriteNameAsync(string name)
        {
            return WriteStringAsync(XmlConvert.VerifyQName(name, ExceptionType.ArgumentException));
        }

        // Writes out the specified namespace-qualified name by looking up the prefix that is in scope for the given namespace.
        public virtual async Task WriteQualifiedNameAsync(string localName, string? ns)
        {
            if (!string.IsNullOrEmpty(ns))
            {
                string? prefix = LookupPrefix(ns);
                if (prefix == null)
                {
                    throw new ArgumentException(SR.Format(SR.Xml_UndefNamespace, ns));
                }
                await WriteStringAsync(prefix).ConfigureAwait(false);
                await WriteStringAsync(":").ConfigureAwait(false);
            }
            await WriteStringAsync(localName).ConfigureAwait(false);
        }

        // XmlReader Helper Methods

        // Writes out all the attributes found at the current position in the specified XmlReader.
        public virtual Task WriteAttributesAsync(XmlReader reader, bool defattr)
        {
            ArgumentNullException.ThrowIfNull(reader);
            return Core(reader, defattr);

            async Task Core(XmlReader reader, bool defattr)
            {
                if (reader.NodeType is XmlNodeType.Element or XmlNodeType.XmlDeclaration)
                {
                    if (reader.MoveToFirstAttribute())
                    {
                        await WriteAttributesAsync(reader, defattr).ConfigureAwait(false);
                        reader.MoveToElement();
                    }
                }
                else if (reader.NodeType != XmlNodeType.Attribute)
                {
                    throw new XmlException(SR.Xml_InvalidPosition, string.Empty);
                }
                else
                {
                    do
                    {
                        // we need to check both XmlReader.IsDefault and XmlReader.SchemaInfo.IsDefault.
                        // If either of these is true and defattr=false, we should not write the attribute out
                        if (defattr || !reader.IsDefaultInternal)
                        {
                            await WriteStartAttributeAsync(reader.Prefix, reader.LocalName, reader.NamespaceURI).ConfigureAwait(false);
                            while (reader.ReadAttributeValue())
                            {
                                if (reader.NodeType == XmlNodeType.EntityReference)
                                {
                                    await WriteEntityRefAsync(reader.Name).ConfigureAwait(false);
                                }
                                else
                                {
                                    await WriteStringAsync(reader.Value).ConfigureAwait(false);
                                }
                            }
                            await WriteEndAttributeAsync().ConfigureAwait(false);
                        }
                    }
                    while (reader.MoveToNextAttribute());
                }
            }
        }

        // Copies the current node from the given reader to the writer (including child nodes), and if called on an element moves the XmlReader
        // to the corresponding end element.
        public virtual Task WriteNodeAsync(XmlReader reader, bool defattr)
        {
            ArgumentNullException.ThrowIfNull(reader);

            if (reader.Settings is { Async: true })
            {
                return WriteNodeAsync_CallAsyncReader(reader, defattr);
            }

            return WriteNodeAsync_CallSyncReader(reader, defattr);
        }


        // Copies the current node from the given reader to the writer (including child nodes), and if called on an element moves the XmlReader
        // to the corresponding end element.
        //use sync methods on the reader
        internal async Task WriteNodeAsync_CallSyncReader(XmlReader reader, bool defattr)
        {
            bool canReadChunk = reader.CanReadValueChunk;
            int d = reader.NodeType == XmlNodeType.None ? -1 : reader.Depth;
            do
            {
                switch (reader.NodeType)
                {
                    case XmlNodeType.Element:
                        await WriteStartElementAsync(reader.Prefix, reader.LocalName, reader.NamespaceURI).ConfigureAwait(false);
                        await WriteAttributesAsync(reader, defattr).ConfigureAwait(false);
                        if (reader.IsEmptyElement)
                        {
                            await WriteEndElementAsync().ConfigureAwait(false);
                        }
                        break;
                    case XmlNodeType.Text:
                        if (canReadChunk)
                        {
                            _writeNodeBuffer ??= new char[WriteNodeBufferSize];
                            int read;
                            while ((read = reader.ReadValueChunk(_writeNodeBuffer, 0, WriteNodeBufferSize)) > 0)
                            {
                                await WriteCharsAsync(_writeNodeBuffer, 0, read).ConfigureAwait(false);
                            }
                        }
                        else
                        {
                            await WriteStringAsync(reader.Value).ConfigureAwait(false);
                        }
                        break;
                    case XmlNodeType.Whitespace:
                    case XmlNodeType.SignificantWhitespace:
                        await WriteWhitespaceAsync(reader.Value).ConfigureAwait(false);
                        break;
                    case XmlNodeType.CDATA:
                        await WriteCDataAsync(reader.Value).ConfigureAwait(false);
                        break;
                    case XmlNodeType.EntityReference:
                        await WriteEntityRefAsync(reader.Name).ConfigureAwait(false);
                        break;
                    case XmlNodeType.XmlDeclaration:
                    case XmlNodeType.ProcessingInstruction:
                        await WriteProcessingInstructionAsync(reader.Name, reader.Value).ConfigureAwait(false);
                        break;
                    case XmlNodeType.DocumentType:
                        await WriteDocTypeAsync(reader.Name, reader.GetAttribute("PUBLIC"), reader.GetAttribute("SYSTEM"), reader.Value).ConfigureAwait(false);
                        break;

                    case XmlNodeType.Comment:
                        await WriteCommentAsync(reader.Value).ConfigureAwait(false);
                        break;
                    case XmlNodeType.EndElement:
                        await WriteFullEndElementAsync().ConfigureAwait(false);
                        break;
                }
            } while (reader.Read() && (d < reader.Depth || (d == reader.Depth && reader.NodeType == XmlNodeType.EndElement)));
        }

        // Copies the current node from the given reader to the writer (including child nodes), and if called on an element moves the XmlReader
        // to the corresponding end element.
        //use async methods on the reader
        internal async Task WriteNodeAsync_CallAsyncReader(XmlReader reader, bool defattr)
        {
            bool canReadChunk = reader.CanReadValueChunk;
            int d = reader.NodeType == XmlNodeType.None ? -1 : reader.Depth;
            do
            {
                switch (reader.NodeType)
                {
                    case XmlNodeType.Element:
                        await WriteStartElementAsync(reader.Prefix, reader.LocalName, reader.NamespaceURI).ConfigureAwait(false);
                        await WriteAttributesAsync(reader, defattr).ConfigureAwait(false);
                        if (reader.IsEmptyElement)
                        {
                            await WriteEndElementAsync().ConfigureAwait(false);
                        }
                        break;
                    case XmlNodeType.Text:
                        if (canReadChunk)
                        {
                            _writeNodeBuffer ??= new char[WriteNodeBufferSize];
                            int read;
                            while ((read = await reader.ReadValueChunkAsync(_writeNodeBuffer, 0, WriteNodeBufferSize).ConfigureAwait(false)) > 0)
                            {
                                await WriteCharsAsync(_writeNodeBuffer, 0, read).ConfigureAwait(false);
                            }
                        }
                        else
                        {
                            //reader.Value may block on Text or WhiteSpace node, use GetValueAsync
                            await WriteStringAsync(await reader.GetValueAsync().ConfigureAwait(false)).ConfigureAwait(false);
                        }
                        break;
                    case XmlNodeType.Whitespace:
                    case XmlNodeType.SignificantWhitespace:
                        await WriteWhitespaceAsync(await reader.GetValueAsync().ConfigureAwait(false)).ConfigureAwait(false);
                        break;
                    case XmlNodeType.CDATA:
                        await WriteCDataAsync(reader.Value).ConfigureAwait(false);
                        break;
                    case XmlNodeType.EntityReference:
                        await WriteEntityRefAsync(reader.Name).ConfigureAwait(false);
                        break;
                    case XmlNodeType.XmlDeclaration:
                    case XmlNodeType.ProcessingInstruction:
                        await WriteProcessingInstructionAsync(reader.Name, reader.Value).ConfigureAwait(false);
                        break;
                    case XmlNodeType.DocumentType:
                        await WriteDocTypeAsync(reader.Name, reader.GetAttribute("PUBLIC"), reader.GetAttribute("SYSTEM"), reader.Value).ConfigureAwait(false);
                        break;

                    case XmlNodeType.Comment:
                        await WriteCommentAsync(reader.Value).ConfigureAwait(false);
                        break;
                    case XmlNodeType.EndElement:
                        await WriteFullEndElementAsync().ConfigureAwait(false);
                        break;
                }
            } while (await reader.ReadAsync().ConfigureAwait(false) && (d < reader.Depth || (d == reader.Depth && reader.NodeType == XmlNodeType.EndElement)));
        }

        // Copies the current node from the given XPathNavigator to the writer (including child nodes).
        public virtual Task WriteNodeAsync(XPathNavigator navigator, bool defattr)
        {
            ArgumentNullException.ThrowIfNull(navigator);
            return Core(navigator, defattr);

            async Task Core(XPathNavigator navigator, bool defattr)
            {
                int iLevel = 0;

                navigator = navigator.Clone();

                while (true)
                {
                    bool mayHaveChildren = false;
                    XPathNodeType nodeType = navigator.NodeType;

                    switch (nodeType)
                    {
                        case XPathNodeType.Element:
                            await WriteStartElementAsync(navigator.Prefix, navigator.LocalName, navigator.NamespaceURI).ConfigureAwait(false);

                            // Copy attributes
                            if (navigator.MoveToFirstAttribute())
                            {
                                do
                                {
                                    IXmlSchemaInfo? schemaInfo = navigator.SchemaInfo;
                                    if (defattr || (schemaInfo == null || !schemaInfo.IsDefault))
                                    {
                                        await WriteStartAttributeAsync(navigator.Prefix, navigator.LocalName, navigator.NamespaceURI).ConfigureAwait(false);
                                        // copy string value to writer
                                        await WriteStringAsync(navigator.Value).ConfigureAwait(false);
                                        await WriteEndAttributeAsync().ConfigureAwait(false);
                                    }
                                } while (navigator.MoveToNextAttribute());
                                navigator.MoveToParent();
                            }

                            // Copy namespaces
                            if (navigator.MoveToFirstNamespace(XPathNamespaceScope.Local))
                            {
                                await WriteLocalNamespacesAsync(navigator).ConfigureAwait(false);
                                navigator.MoveToParent();
                            }
                            mayHaveChildren = true;
                            break;
                        case XPathNodeType.Attribute:
                            // do nothing on root level attribute
                            break;
                        case XPathNodeType.Text:
                            await WriteStringAsync(navigator.Value).ConfigureAwait(false);
                            break;
                        case XPathNodeType.SignificantWhitespace:
                        case XPathNodeType.Whitespace:
                            await WriteWhitespaceAsync(navigator.Value).ConfigureAwait(false);
                            break;
                        case XPathNodeType.Root:
                            mayHaveChildren = true;
                            break;
                        case XPathNodeType.Comment:
                            await WriteCommentAsync(navigator.Value).ConfigureAwait(false);
                            break;
                        case XPathNodeType.ProcessingInstruction:
                            await WriteProcessingInstructionAsync(navigator.LocalName, navigator.Value).ConfigureAwait(false);
                            break;
                        case XPathNodeType.Namespace:
                            // do nothing on root level namespace
                            break;
                        default:
                            Debug.Fail($"Unexpected node type {nodeType}");
                            break;
                    }

                    if (mayHaveChildren)
                    {
                        // If children exist, move down to next level
                        if (navigator.MoveToFirstChild())
                        {
                            iLevel++;
                            continue;
                        }

                        // EndElement
                        if (navigator.NodeType == XPathNodeType.Element)
                        {
                            if (navigator.IsEmptyElement)
                            {
                                await WriteEndElementAsync().ConfigureAwait(false);
                            }
                            else
                            {
                                await WriteFullEndElementAsync().ConfigureAwait(false);
                            }
                        }
                    }

                    // No children
                    while (true)
                    {
                        if (iLevel == 0)
                        {
                            // The entire subtree has been copied
                            return;
                        }

                        if (navigator.MoveToNext())
                        {
                            // Found a sibling, so break to outer loop
                            break;
                        }

                        // No siblings, so move up to previous level
                        iLevel--;
                        navigator.MoveToParent();

                        // EndElement
                        if (navigator.NodeType == XPathNodeType.Element)
                            await WriteFullEndElementAsync().ConfigureAwait(false);
                    }
                }
            }
        }

        // Element Helper Methods

        // Writes out an attribute with the specified name, namespace URI, and string value.
        public async Task WriteElementStringAsync(string? prefix, string localName, string? ns, string value)
        {
            await WriteStartElementAsync(prefix, localName, ns).ConfigureAwait(false);
            if (!string.IsNullOrEmpty(value))
            {
                await WriteStringAsync(value).ConfigureAwait(false);
            }
            await WriteEndElementAsync().ConfigureAwait(false);
        }

        // Copy local namespaces on the navigator's current node to the raw writer. The namespaces are returned by the navigator in reversed order.
        // The recursive call reverses them back.
        private async Task WriteLocalNamespacesAsync(XPathNavigator nsNav)
        {
            string prefix = nsNav.LocalName;
            string ns = nsNav.Value;

            if (nsNav.MoveToNextNamespace(XPathNamespaceScope.Local))
            {
                await WriteLocalNamespacesAsync(nsNav).ConfigureAwait(false);
            }

            if (prefix.Length == 0)
            {
                await WriteAttributeStringAsync(string.Empty, "xmlns", XmlReservedNs.NsXmlNs, ns).ConfigureAwait(false);
            }
            else
            {
                await WriteAttributeStringAsync("xmlns", prefix, XmlReservedNs.NsXmlNs, ns).ConfigureAwait(false);
            }
        }

        public async ValueTask DisposeAsync()
        {
            await DisposeAsyncCore().ConfigureAwait(false);
            Dispose(false);
            GC.SuppressFinalize(this);
        }

        protected virtual ValueTask DisposeAsyncCore()
        {
            if (WriteState != WriteState.Closed)
            {
                Dispose(true);
            }
            return default;
        }
    }
}
